Nitrogen (N) is an important plant nutrient and is crucial for the plant growth and grain yield formation of field crops such as wheat (Triticum aestivum L. ssp. aestivum). However, little is known about the influence of N on secondary metabolites in wheat grains which are supposed to be beneficial for human health due to their antioxidant potentials. Therefore, we investigated the influence of N fertilization on plant growth and yield performance of winter wheat, as well as on total phenolic concentration, antioxidant capacity, and the accumulation of (in)soluble phenolic acids in wheat grains during the grain‐filling phase. It was found that ferulic acid was the predominant phenolic acid in wheat grains. As expected, higher amounts of N fertilizer led to increasing grain yields, whereas the concentration of soluble ferulic acid decreased. In contrast, insoluble bound ferulic acid, total phenolic content, and antioxidant capacity were not affected by the N treatment. Insoluble phenolic compounds seemed to be less susceptible to variations in N supply.

This work investigated the influence of N fertilization and grain maturity on total phenolic concentration (TPC) of wheat caryopses. A pot experiment was conducted, using soft spring wheat (Triticum aestivum cv. Thasos) which was treated with four different amounts of nitrogen (0.25–2.00 g N pot−1) and harvested at three different development stages (medium milk stage, late milk stage, and dough maturity). Phenolic compounds were extracted and analyzed as total phenolic concentration in three discrete fractions: free soluble, conjugated soluble and insoluble bound forms. TPC of free phenolic compounds rose with increasing N supply while TPC of conjugated soluble phenolics decreased at the same time. Insoluble phenolics were less affected by N treatment. Total phenolic concentration also changed with the development stage of caryopses and reached a peak at the late milk stage.

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Wheat is a field crop with high relevance for food production worldwide. An adequate supply with nitrogen (N) is crucial for the grain yield and grain quality of wheat. However, little is known about the influence of N fertilization on phenolic compounds, such as phenolic acids and flavonoids, in the leaves of wheat (Triticum aestivum L. ssp. aestivum cv. Genius) under field conditions. Therefore, a field experiment was set up with winter wheat grown under different N fertilization regimes to investigate the influence of N supply on antioxidant properties in general as well as on distinct phenolic acids and flavonoids in the leaves of wheat plants. In the present study, total phenolic concentration and antioxidant capacity were negatively influenced by higher dosages of N fertilizer. Antioxidant properties were mainly determined by chlorogenic acid and homoorientin, a phenolic acid and a flavonoid, respectively. The production of these phenolic compounds was not limited by the gene transcription of phenylalanine ammonia lyase or cinnamate 4‐hydroxylse, the key enzymes of the phenylpropanoid pathway, since the transcription of these enzymes was not significantly influenced by N fertilization.

P-type ATPases, as major consumers of cellular ATP in eukaryotic cells, are characterized by the formation of a phosphorylated enzyme intermediate (E2P), a process that is allosterically coupled to translocation of cations against an electrochemical gradient. The catalytic cycle comprises binding of Mg-ATP at the nucleotide-binding domain, phosphorylation of the E1 state (E1), conformational transition to the E2P state, and dephosphorylation through the actuator domain and re-establishment of the E1 state. Recently, it has been suggested that, for several P-type ATPases, Mg-ATP binds to the phosphorylated enzyme, thereby accelerating the transition to the E1 state, before then becoming the enzyme's catalytic substrate. Here, we provide evidence supporting this viewpoint. We employed kinetic models based on steady-state kinetics in the presence and absence of the reversible inhibitor orthovanadate. Vanadate is generally considered to be a conformational probe that specifically binds to the E2 state, arresting the enzyme in a state analogous to the E2P state. Hydrolytic H + -ATPase activities were measured in inside-out plasma membrane vesicles isolated from roots and shoots of maize plants. For root enzymes, kinetic models of vanadate inhibition that allow simultaneous binding of Mg-ATP and vanadate to the same enzyme state were most plausible. For shoot enzymes, application of the competitive inhibitor Mg-free ATP attenuated vanadate inhibition, which is consistent with a model in which either Mg-free ATP or Mg-ATP is bound to the enzyme when vanadate binds. Therefore, data from roots and shoots indicate that binding of ATP species before transition to the E1 state plays an important role in the catalytic cycle of plant plasma membrane H + -ATPase.